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Engine Rear Mains Seal - 2019

The standard Lancia crankshaft seal is a simple Archimedes-Type thread/scroll seal/oil slinger, that relies on the slight clearance between the crank and the engine block to stop oil escaping out the rear. However, my Aprilia's engine had been modified back in the UK to take modern oil seals, both at the rear and the front of the crank, see examples below. (click on an image to enlarge)

This had worked very well for years with just a slight leak from the rear after a long run. But disaster was just around the corner. If you look back at the engine rebuild pages the engine came out and was disassembled and reassembled on a number of occasions and during one of these I managed to knock the alloy housing for the rear seal out of alignment so that it was hit by the crankshaft studs that hold the flywheel on. The next set of photos show the damage to the housing and the melted oil seal.

My first attempt to fix the damage I "repaired" the housing and on external advice fitted a hydraulic seal, the seal lasted about five minutes before tearing itself to pieces. For the second attempt I again "repaired' the housing and fitted a SKF 22328 seal, an oil seal with an outside metal casing, this again failed and destroyed the alloy housing as well.

Of course every time the above happend I had to take the engine out of the car, maybe one day I'll build an engine test stand!

So with the housing destroyed I had to turn up a new one. As the housing is split this meant making two identical copies to offset cut to fit as one complete unit, I made three just in case. Also I did more research on the best type of seal and this time got proper expert advice and bought a couple of Viton high pressure seals and viton O rings for the external housing seal. Sealnet in Brisbane had the type and correct size.

Next was the task of fitting the new seal/housing combination. The seal has to be cut in half to slide over the crankshaft. The original alloy housing had a single locating pin, on my new one I fitted two pins to prevent any chance of it moving into the crank studs. It all went together very well and the first time the engine ran there was minimal vibration and lots of power, BUT there was still a big oil leak coming out the rear. This whole thing was getting very boring and depressing.

So the engine had to come out again, the sixth time in total during this whole debacle. Luckily this time the seal and housing were fine, the oil was simply leaking out of a gap between the block and the sump that had not been sealed correctly, by me! So the fix was relatively simple, use lots of Threebond 1207C liquid gasket, put it all back together carefully and all was finally well.

Running the engine there is a vibration period around the 3200-3500 rpm in all gears, plus there is still a minor oil leak. Both these are issues I can live with for now.

In summary I started the engine rebuild on November 6 2017 and finished on November 20 2019. In the end the whole process got me down, I lost faith in the car and in myself. The car didn't go to Castlemaine in October 2019 and with the terrible summer we've had and now Coronavirus thrown in the Aprilia has been sitting in the garage for a few months while I get my head back together and find the enthusiasm I used to have for this little pain in the bum.


March 2020